No Viewfinder Box / Blender renders out entire scene
Few things come to mind:

You may have pressed / and entered local view. This will allow you to only view (in the viewport) the objects you had selected when you pressed the key. This does not affect renders or the hidden/shown state of objects.

If you've hidden the objects by pressing the "eye" icon, you've only hidden the objects from the viewport. If you pres the Filter button which looks like a funnel, you can see all the restriction toggles.

If you enable the icon with the camera, you'll see that camera icon next to each object. Toggling that will show/hide an object from the render.